With cross-platform video chatting in place, WhatsApp is offering a combination of video and text messages in one app, similar to what is found in Microsoft’s Skype, Snap Inc.’s Snapchat and Facebook Messenger. Chatters won’t have to wonder what OS their friends are on when they go to chat face to face. (The software also competes with Apple’s proprietary FaceTime and Google’s Duo app for iOS and Android.)

The launch Tuesday—in an app update for iOS 8 or newer, Android 4.1 or newer and both Windows 10 Mobile and Windows Phone 8.1—will bring video calling to over 1 billion WhatsApp users across more than 180 countries on the same day, said Manpreet Singh, WhatsApp’s lead engineer.

Like Apple’s FaceTime and iMessage apps, WhatsApp offers a security feature called end-to-end encryption that’s turned on by default for text, voice and now video messaging. End-to-end encryption means the transmission is encrypted even on WhatsApp’s own servers, so it would be equally obscured from hackers and government agencies, and would be hard for WhatsApp to divulge, even with a court order. It’s a ruler-shaped touch screen that lives above the keyboard on

Online privacy experts consider WhatsApp’s choice of encryption technology to be among the best available. It’s also what took WhatsApp, which made its text-messaging debut six years ago, so long. Many rivals only offer encryption as a limited option. “It’s harder to build something that’s on for everyone all at once,” Mr. Singh said.

While privacy is a highly touted value for WhatsApp, the messaging service shares some user data —such as the phone number tied to your user account—with its parent company, Facebook. With end-to-end encryption, however, neither WhatsApp nor Facebook can see any content from messages and video calls, Mr. Singh said.